This disclosure generally relates to a system and method for controlling evaporative emissions of a volatile fuel such that a fuel tank can be isolated from a fuel vapor collection canister while purging the fuel vapor collection canister.
It is believed that prior to legislation requiring vehicles to store hydrocarbon vapors that are generated when refueling a vehicle, a simple orifice structure was used to maintain a positive pressure in a fuel tank to retard vapor generation. It is believed that such orifice structures could no longer be used with the advent of requirements controlling on-board refueling. It is believed that, on some vehicles, the orifice structure was simply deleted, and on other vehicles, the orifice structure was replaced with a diaphragm-actuated pressure relief valve. It is believed that these diaphragm-actuated valves suffer from a number of disadvantages including that the calibration (i.e., pressure blow-off level) changes with temperature and age.
It is believed that it is necessary on some vehicles to maintain an elevated pressure in the fuel tank to suppress the rate of fuel vapor generation and to minimize hydrocarbon emissions to the atmosphere. It is believed that under hot ambient temperature conditions or when the fuel is agitated, e.g., when a vehicle is operated on a bumpy road, the amount of fuel vapor generated can exceed the amount of fuel vapor that can be purged by the engine. It is believed that a carbon canister can become hydrocarbon saturated if these conditions occur and are maintained for an extended period. It is believed that such a hydrocarbon saturated carbon canister is unable to absorb the additional fuel vapors that occur during vehicle refueling, and that hydrocarbon vapors are released into the atmosphere. A legislated standard has been set for the permissible level of free hydrocarbons that may be released. A so-called xe2x80x9cshed testxe2x80x9d is used to measure the emission of the free hydrocarbons for determining compliance with the legislated standard.
It is believed that there is needed to provide a valve that overcomes the drawbacks of orifice structures and diaphragm-actuated pressure relief valves.
The present invention provides a system for controlling evaporative emissions of a volatile fuel. The system includes a fuel vapor collection canister, a purge valve, an isolation valve, a fuel tank, and a vent valve. The fuel vapor collection canister includes a supply port and a discharge port. The purge valve includes an inlet port and an outlet port. The inlet port of the purge valve is in fluid communication with the discharge port of the fuel vapor collection canister. The isolation valve includes a housing, a valve body, and a seal. The housing has a first port in fluid communication with the supply port of the fuel vapor collection canister, a second port, and a fuel vapor flow path that extends between the first and second ports. The valve body is movable with respect to the housing along an axis between a first configuration and a second configuration. The first configuration permits substantially unrestricted fuel vapor flow between the first and second ports, and the second configuration substantially prevents fuel vapor flow between the first and second ports. The seal, which is located at an interface between the housing and the valve body, includes an annular lip that projects obliquely toward the axis in the first configuration. The fuel tank is in fluid communication with the second port of the isolation valve. The vent valve controls ambient fluid flow with respect to the fuel vapor collection canister.
The present invention also provides a system for controlling evaporative emissions of a volatile fuel. The system includes a fuel vapor collection canister, a purge valve, a fuel tank, means for isolating the fuel tank from the purge valve, and a vent valve. The fuel vapor collection canister includes a supply port and a discharge port. And the purge valve includes an inlet port and an outlet port. The inlet port of the purge valve is in fluid communication with the discharge port of the fuel vapor collection canister. The vent valve controls ambient fluid flow with respect to the fuel vapor collection canister.
The present invention also provides a method for controlling evaporative emissions of a volatile fuel. The volatile fuel is stored in a fuel tank and is combusted in an internal combustion engine. The method includes accumulating fuel vapor in a fuel vapor collection canister; providing an isolation valve in a first conduit, providing a purge valve in a second conduit, providing a vent valve that controls ambient fluid flow with respect to the fuel vapor collection canister, and isolating the fuel tank from the fuel vapor collection canister while purging the fuel vapor collection canister. The first conduit provides fuel vapor communication between the fuel tank and the fuel vapor collection canister. The second conduit provides fuel vapor communication between the fuel vapor collection canister and the internal combustion engine. The isolating includes the isolation valve substantially preventing fuel vapor flow through the first conduit and the vent valve permitting ambient fluid flow in to the fuel vapor collection canister. And the purging includes the purge valve permitting generally unrestricted fuel vapor flow through the second conduit.